1. Field of the Invention
The present invention relates to a vehicle which can turn with a smaller turning radius.
2. Description of the Related Art
For four-wheel vehicles, a parameter called the xe2x80x9cturning radiusxe2x80x9d is known for indicating the performance of each four-wheel vehicle. A vehicle having a smaller turning radius can make a smaller turn at a corner during a turning operation such as U-turn.
Vehicles employing four-wheel steering (4WS) have been known as prior art four-wheel vehicles which can improve the turning radius. The 4WS refers to a system which controls the steering angle (rudder angle) of not only front wheels but also rear wheels in association with a manipulation through a steering wheel. The 4WS system can reduce the turning radius due to the controllable steering angle provided to the rear wheels .
A fifth wheel system is also known as an improvement in the turning radius. The fifth wheel system additionally has a fifth wheel stored below the floor, in addition to four wheels, such that the fifth wheel is slightly protruded relative to the other wheels during a turn to lift up the vehicle body, and the fifth wheel is driven to have the vehicle make a turn.
However, the 4WS, while it is effective in reducing the turning radius, suffers from limitations to the reduction in the turning radius because the steering angle is limited in order to suppress an inherent shake-out phenomenon to a practically ignorable extent. The fifth wheel system in turn is expected to provide significant effects, but implies a problem that the vehicle becomes unstable due to a three-wheel state during a turning operation.
Moreover, because a vehicle turning operation which reduces the turning radius requires actuation of a turning mechanism which cannot be used during a normal running operation such as straight traveling and backward traveling, the vehicle presents another problem in that it has only limited operation states in which the vehicle can be turned with stability.
In addition, a vehicle, when equipped with such a turning mechanism, has been desired to provide improved operability during a turning operation.
It is therefore an object of the present invention to provide a vehicle which is capable of turning a vehicle body with a relatively small turning radius and a good operability during a turning operation.
A vehicle equipped with a turning mechanism according to the present invention comprises rotatably supporting means for supporting one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, for rotation concerning respective axes perpendicular to the ground; rotating position fixing means for fixing the one pair of left and right wheels at respective angular positions along tangential directions of an arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, and having the center located near a center point of a rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels; and turn driving means for applying a rotating torque to the one pair of left and right wheels at the angular positions fixed by the rotating position fixing means to turn a vehicle body on a neighborhood of the center point of the rotating axle for running the vehicle of the other pair of left and right wheels.
According to the vehicle of the present invention described above, because one of the front and rear pairs of left and right wheels, to which a running torque produced by the driving source is not transmitted, are supported for rotation concerning respective axes perpendicular to the ground, and the one pair of left and right wheels are fixed at the respective angular positions along the tangential directions of the arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center of the arc located near the center point of the rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels, it is possible to provide a relatively simple and small turning mechanism. In addition, because the radius of the arc passing the axes of the one pair of left and right wheels perpendicular to the ground and having the center near the center point of the rotating axle of the other pair of left and right wheels is the turning radius when the vehicle is turned, the turning radius is extremely small.
Another vehicle equipped with a turning mechanism according to the present invention comprises steering means rotatably arranged for steering the vehicle; detecting means for detecting a manipulating state of the steering means; mode selecting means for selecting one of a normal mode for running the vehicle and a turn mode for turning a vehicle body while the vehicle stops running; steering control means for changing a steering angle of a steering wheel of the vehicle in accordance with a result of detection by the detecting means when the mode selecting means selects the normal mode; and turning means for turning the vehicle body on a neighborhood of the center point of an axle extending between a front or rear pair of left and right wheels of the vehicle in response to a result of detection by the detecting means, without allowing the steering control means to change the steering angle of the steering wheel in accordance with a result of detection by the detecting means when the mode selecting means selects the turn mode.
According to the vehicle of the present invention described above, the vehicle body is turned on a point near the center point of the rotating axle of the front or rear left and right wheels of the vehicle, thereby making it possible to turn the vehicle body with a relatively small turning radius. In addition, the steering means such as the steering wheel for use in the normal mode for running the vehicle is also used in the turn mode to perform the turning operation, the operability can be improved during the turning operation. Furthermore, the utilization of the steering means for the turning operation can reduce the cost as compared with a manipulating device such as a switch which would be newly provided for the turning operation.
The turning means includes rotatably supporting means for supporting one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, for rotation concerning respective axes perpendicular to the ground; determining means for determining whether a vehicle operating state satisfies predetermined conditions when the turn mode is selected; and rotation driving means, when the determining means determines that the predetermined conditions are satisfied, for rotating the one pair of left and right wheels from straight traveling positions taken when the vehicle is running to respective angular positions along tangential directions of an arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, the arc having the center located near a center point of a rotating axle of the other of the front and rear pairs of left and right wheels.
According to the vehicle described above, because one of the front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, are supported for rotation concerning the respective axes perpendicular to the ground, and the one pair of left and right wheels are rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential direction of the arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center of the arc located near the center point of the rotating axle of the other of the front and rear pairs of left and right wheels, it is possible to provide a relatively simple and small turning mechanism. In addition, since he one pair of left and right wheels will not be rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential directions for a turning operation unless the vehicle operating state satisfies the predetermined conditions suitable for a turn in the turn mode, the turning operation can be performed while the vehicle is in a stable state.
The turn driving means turns the vehicle body over an angular distance corresponding to the rotating direction and the rotating angle of the steering means detected by the detecting means. According to this configuration, the vehicle body is turned in a direction in which the driver rotates the steering means, causing the vehicle to turn over an angular distance corresponding to a rotating angle determined by the driver, thereby making it easy to turn the vehicle body to a desired position in a turning operation with an extremely favorable operability resulting therefrom.
In the configuration described above, the turn driving means turns the vehicle body at a speed corresponding to the rotating direction and the rotating angle of the steering means detected by the detecting means. According to this configuration, the vehicle body is turned in a direction in which the driver rotates the steering means, causing the vehicle to turn at a speed corresponding to a rotating angle determined by the driver, so that the vehicle body is smoothly turned in a turning operation with an extremely favorable operability.
The predetermined conditions include at least the following conditions:
(a) the vehicle stops running; and
(b) the steering angle of the front wheels is substantially zero degrees.
By defining the predetermined conditions as mentioned, it is possible to confirm whether or not the vehicle is in a state from which the vehicle can transition without any problem to a vehicle body turning operation for which the one pair of left and right wheels are driven to rotate.
The condition defining that the vehicle stops running is detected from a shift position of a transmission equipped in the vehicle lying in a P (parking) position or an N (neutral) position, or a side brake being in operation. According to this configuration, it is possible to detect that the vehicle is not merely temporarily stopped, thereby preventing the vehicle from running forward or backward during a turning operation.
Also, the vehicle further comprises a shift lock mechanism for disabling the transmission to perform a shifting operation when at least the one pair of left and right wheels are at positions other than the straight traveling positions. According to this configuration, since the vehicle is disabled to travel straight by the shift lock mechanism when the one pair of left and right wheels are at the angular positions rotated from the straight traveling positions for turning the vehicle body, it is possible to prevent erroneous manipulations by the driver.
The turn driving means applies the rotating torque to the one pair of left and right wheels with a driving source different from the driving source to turn the vehicle body. According to this configuration, unlike a normal driving source for running, a driving source capable of producing a minimally required driving force is sufficient, so that a smaller driving source can be driven for the turning operation in order to save the space.
The rotatably supporting means includes a trailing arm for rotatably supporting the one pair of left and right wheels through knuckles at the respective axes perpendicular to the ground of the one pair of left and right wheels. According to this configuration, since the rotatably supporting means is formed of existing suspension members, neither dedicated parts nor members are required for use in implementing the rotatably supporting means, thereby making it possible to reduce the cost.
The turn driving means includes braking means for applying a braking force to rotations of the one pair of left and right wheels in response to a manipulation on a switch arranged in the steering wheel. According to this configuration, the driver can stop turning the vehicle body by manipulating the switch while holding the steering wheel.
Further, the turn driving means includes braking means for applying a braking force to rotations of the one pair of left and right wheels in response to the driver stepping on a brake pedal. With this configuration, the driver can stop turning the vehicle body by stepping on the brake pedal in a manner similar to in the normal mode, thereby making it possible to readily stop turning the vehicle body at a desired position.
The turning means further includes rotatably supporting means for supporting one of front and rear pairs of left and right wheels, to which a running torque produced by a driving source is not transmitted, for rotation concerning respective axes perpendicular to the ground; determining means for determining whether a vehicle operating state satisfies predetermined conditions when the turn mode is selected; rotation driving means, when the determining means determines that the predetermined conditions are satisfied, for rotating the one pair of left and right wheels from straight traveling positions taken when the vehicle is running to respective angular positions along tangential directions of an arc passing the axes perpendicular to the ground of the one pair of left and right wheels, the arc having the center located near a center point of a rotating axle of the other of the front and rear pairs of left and right wheels; and turn driving means for applying rotating torques in rotating directions different from each other to the left and right wheels of the other pair at the angular positions along the tangential directions in accordance with a result of detection by the detecting means to turn the vehicle body on a neighborhood of the center point of the rotating axle of the other pair of left and right wheels.
According to the turning means configured as described above, one of front and rear pairs of left and right wheels, to which a running torque produced by the driving source is not transmitted, are supported for rotation concerning the respective axes perpendicular to the ground, and the one pair of left and right wheels are rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential directions of the arc passing the respective axes perpendicular to the ground of the one pair of left and right wheels, with the center of the arc located near the center point of the rotating axle of the other of the front and rear pairs of left and right wheels, thereby making it possible to provide a relatively simple and small turning mechanism. In addition, since the one pair of left and right wheels will not be rotated from the straight traveling positions taken when the vehicle is running to the respective angular positions along the tangential directions for a turning operation unless the vehicle operating state satisfies the predetermined conditions suitable for a turn in the turn mode, the turning operation can be performed while the vehicle is in a stable state. Further, since the rotating torques are applied to the left and right wheels of the other pair at the angular positions along the tangential directions to turn the vehicle body on a neighborhood of the center point of the rotating axle of the other pair of left and right wheels, the turning radius is extremely small when the vehicle is turned.
The turn driving means applies the rotating torques in rotating directions different from each other to the respective left and right wheels of the other pair with a driving source different from the driving source to turn the vehicle. According to this configuration, like the aforementioned case, a driving source capable of producing a minimally required driving force is sufficient unlike a normal driving source for running, so that a smaller driving source can be driven for the turning operation in order to save the space.
The turn driving means further includes means for fixing a case for rotatably supporting two pinions arranged in a differential during a turning operation of the vehicle body, and a motor for driving one of side gears arranged in the differential. According to this configuration, since a differential function, i.e., rotation of the one driving axle with the case of the differential maintained fixed causes the other driving axle to reversely rotate, can be effectively utilized, a diving force for turning the vehicle body can be provided only by adding a minimally required function.